The present invention extends to processing solid material by heating or by cooling.
The present invention relates particularly, although by no means exclusively, to processing a charge of solid material (which, optionally, has a low thermal conductivity) in a vessel under conditions (which include high pressure and temperature) that produce liquid from the solid material and high mass flow rate of gas (produced from the solid material and/or added to the vessel as part of the process).
The present invention relates more particularly to a process and an apparatus for upgrading carbonaceous materials, typically coal, particularly low rank coal, under conditions which include high pressure and temperature to increase the BTU value of the carbonaceous materials by removing water from the carbonaceous materials, which process and apparatus includes separating solids, liquid, and gas phases produced by or supplied to the process.
The following discussion of the prior art is in relation to difficulties separating solids, gas and liquid phases produced when coal is dewatered by heating the coal under elevated pressure conditions. It is noted that in more general terms the present invention extends to difficulties caused by high mass flow rate of gas through vessels containing solids, with or without liquid present, under heating or cooling conditions.
U.S. Pat. No. 5,290,523 to Koppelman discloses a process for upgrading coal by the simultaneous application of pressure and temperature.
Koppelman discloses thermal dewatering of coal by heating coal under conditions which include elevated pressure and temperature to cause physical changes in the coal that results in water being removed from the coal by a "squeeze" reaction.
Koppelman also discloses maintaining the pressure sufficiently high during the upgrading process so that the by-product water is produced mainly as a liquid rather than steam.
Koppelman also discloses a range of different apparatus options for carrying out the upgrading process. In general terms, the options are based on the use of a pressure vessel which includes an inverted conical inlet, a cylindrical body, a conical outlet with a single outlet at the apex of the conical outlet, ie the lowest section of the vessel, and an assembly of vertically or horizontally disposed heat exchange tubes positioned in the body.
In one proposal to use a Koppelman-type apparatus, the vertically disposed tubes and the outlet end are packed with coal, and nitrogen is injected to pressurise the tubes and the outlet end. The coal is heated by indirect heat exchange with a heat exchange medium supplied to the cylindrical body externally of the tubes. Further heat is generated by supplying water to the tubes, which subsequently forms steam that acts as a heat transfer medium. The combination of elevated pressure and temperature conditions evaporates some of the water from the coal and thereafter condenses some of the water as a liquid. A portion of the steam generated following the addition of water also condenses as a liquid due to the elevated pressure. Steam which is not condensed, and which is in excess of the requirements for optimum pressurisation of the packed bed, must be vented. In addition, noncondensable gases (eg CO, CO.sub.2) are evolved and need to be vented. Periodically, liquid is drained from the outlet end. Finally, after a prescribed residence time, the vessel is depressurised and the upgraded coal is discharged via the same outlet end.
It has been found that the configuration of the outlet end of the above-described Koppelman-type apparatus has not been altogether satisfactory in terms of separating the solid/liquid/gas phases and, more particularly liquid/gas phases. The problems encountered include high pressure drop and high gas velocity in the outlet end which results in:
(i) two phase flow of liquid and gas from the outlet end that is difficult to control; PA1 (ii) blockage preventing discharge; and PA1 (iii) fine and sometimes coarse material being discharged with liquid (and gas). PA1 (a) a vessel having: PA1 (b) a means for supplying a fluid to pressurise the packed bed; and PA1 (c) a means for supplying a heat exchange medium to heat the solid material in the packed bed. PA1 (i) the need to progressively remove gas at different levels down the outlet end such that the mass flow per unit cross section (or velocity) in the packed bed is maintained approximately constant at each level; PA1 (ii) the need to draw gas at each level towards a gas outlet without creating regions of high gas velocity which may lead to high pressure drop and/or entrainment of solids and/or liquid; and PA1 (ii) the need to turn the gas flow from downward to outward lateral flow whilst at the same time allowing any liquid to continue in a substantially downward direction. PA1 (a) supplying the solid material to a vessel to form a packed bed of the solid material; PA1 (b) pressurising the packed bed; PA1 (c) heating the solid material by heat exchange with a heat exchange medium, whereby the combined effect of pressure and heat is to release water and other liquid and/or gaseous compounds from the, solid material, with part of the released water being in a gas phase and part of the water being in a liquid phase; PA1 (d) discharging gas from the packed bed via at least one gas outlet in the vessel; and PA1 (e) discharging liquid from the packed bed via a liquid outlet in the vessel located below the gas outlet. PA1 (i) the pressure drop in the outlet end; and/or PA1 (ii) the flow of gas into the section of the outlet end that is below the level of the gas outlet.
More particularly, in general terms, gas and liquid exiting a vessel through the same outlet duct tend to flow in a most irregular fashion due to the different flow resistances of the gas and liquid in the bed, ducts and control valves. The compressible nature of the gas, the rapidly varying resistances, and the comparatively high density of the liquid leads to a flow with high acceleration forces which can lead to disturbance and probable transport of particles in the packed bed.
One object of the present invention is to provide improved separation of solids, liquid, and gas generated in or supplied to the Koppelman-type apparatus.
A more general object of the present invention is to provide an apparatus for separating solids, liquid, and gas in pressure vessels operated at high pressures and temperatures.
A further more general object of the present invention is to provide an apparatus for introducing and/or removing high mass flow rate of gas into and/or from vessels containing solid material which is being processed in the vessels.
The term "high" in the context of "mass flow rate of gas" is understood herein as indicating that the total amount of the gas is a significant proportion, typically 5-10%, of the mass of the solid material and/or that the mass flow rate of gas approaches the threshold for fluidising the solid material in the vessel.
In the broadest sense, the present invention provides an improvement to a vessel for processing a charge of solid material under conditions which include high mass flow rate of gas through the vessel, the improvement including providing the vessel with at least one solids outlet for discharging solids from the vessel and a plurality of gas inlets and/or gas outlets for introducing gas into or discharging gas from the vessel at one or more levels of the vessel above the gas outlet or outlets.
More particularly, according to the present invention there is provided an improvement to a vessel for processing a charge of solid material under conditions which include high mass flow rate of gas through the vessel and which produce liquid from the solid material, the improvement including an outlet end of the vessel having at least one solids outlet, at least one liquids outlet, and at least one gas outlet, and the at least one gas outlet being positioned above the at least one solids outlet and the at least one liquid outlet.
The aspect of the present invention described in the preceding paragraph is based on the realisation that effective separation of solids, liquid, and gas from a vessel, with minimum entrainment of solids and gas with liquid, can be achieved by providing separate removal of liquid and gas at different levels of the outlet end, and with the gas outlet (or outlets) being at a higher level than that of the liquid outlet (or outlets).
This aspect of the present invention can also be described as an apparatus for processing a charge of a solid material under conditions which include high mass flow rate of gas through the apparatus and which produce liquid from the solid material, which apparatus includes:
(i) an inlet end having an inlet for supplying the solid material to form a packed bed in the vessel; and PA2 (ii) an outlet end having at least one solids outlet, at least one liquids outlet, and at least one gas outlet positioned above the solids/liquid outlets;
It is preferred that the outlet end be in a lower section of the vessel.
It is preferred that the outlet end converges to one (or possibly more) solids outlets.
It is preferred particularly that the outlet end be conical.
It is preferred that the outlet end includes a plurality of gas outlets.
It is preferred that the gas outlets be located at more than one level of the outlet end.
It is preferred that there be a plurality of gas outlets at least at one level of the outlet end.
Preferably, at each level that has a plurality of gas outlets, the gas outlets are spaced around the perimeter of the vessel so that across that level there is substantially uniform downward mass flow rate of gas.
In more general terms, the number and location and structure of the gas outlets is governed by:
It is noted that the term "fluid" as used in paragraph (b) above is sufficiently broad to cover the use of a gas, such as nitrogen, and a liquid, such as water, introduced into the vessel.
It is preferred that the means for supplying the heat exchange medium supplies the medium to heat the solid material by indirect heat exchange.
It is preferred that the vessel be a pressure vessel.
The above-described particular aspect of the present invention can also be described as a process for processing a charge of a solid material under conditions which include high mass flow rate of gas and which produce liquid from the solid material, which process includes:
The process may include introducing gas to the vessel as a working fluid to contribute to heat transfer to the solid material.
It is noted that step (d) of discharging gas may include removal of an amount of liquid. It is also noted that step (e) of discharging liquid may include removal of an amount of gas.
It is preferred that the basis for discharging gas from the packed bed be to control:
It is preferred particularly that the process includes discharging gas from the packed bed via a plurality of gas outlets so that there is substantially constant flow velocity of gas in the section of the outlet end below the level of the gas outlets.
It is preferred that the basis for discharging liquid from the packed bed be the level of liquid in the outlet end at any point in time during operation of the process such that discharge via the liquid outlet is predominantly liquid.
It is preferred that the process includes discharging gas from the packed bed via gas outlets at two or more levels above the liquid outlet.
It is preferred that the process includes discharging gas via a plurality of gas outlets at least at one of the levels above the liquid outlet.
It is preferred that the vessel includes an outlet end that converges to one (or possibly more) solids outlets.
It is preferred particularly that the vessel includes a conical outlet end and that the gas outlet or outlets and the liquid outlet be located in the outlet end.